The business secretary, Greg Clark, is a member of the prime minister’s Brexit committee.
Photograph: Daniel Leal-Olivas/AFP/Getty Images

Several cabinet members have aligned themselves with Philip Hammond in cautioning against the risks of a “hard Brexit”, with sources suggesting these allies include the business secretary, Greg Clark, and the work and pensions secretary, Damian Green.

The chancellor has been accused by ministers who supported Brexit before the referendum of attempting to undermine the process, in particular by urging a delay on migration curbs amid fears of the impact if Britain loosens its economic ties with the EU too dramatically.

But Whitehall sources have confirmed that Hammond is not a “lone voice” inside government, with several other cabinet figures who supported the remain campaign calling on the prime minister to keep open the possibility of close economic ties with the EU.

No 10 plays down cabinet differences over Brexit

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Clark and Green, who are both on May’s Brexit committee, are said to have been making their case behind closed doors. Other senior colleagues, including the education secretary, Justine Greening, are also thought to be supportive of Hammond’s stance, which is focused on maintaining as much access as possible to the single market as the UK quits the EU.

Amber Rudd, the home secretary, who is drawing up proposals for immigration controls but was an enthusiastic supporter of the EU before the June referendum, has made some supportive arguments in cabinet discussions backing the chancellor.

One official said that while the cabinet ministers accepted that Britain must leave the EU and that immigration controls would be part of that process, they were pushing May to avoid opting for an overly hard Brexit. “There are shades of grey,” said the source, who argued that there were ways to control freedom of movement without automatically losing economic links with the EU. “Remainers are vocal behind closed doors, just not in the newspapers.”

One senior MP praised the chancellor as “incredibly courageous” for highlighting the risks of Brexit in cabinet meetings. They said a number of cabinet members and more junior ministers backed him but were nervous about speaking out publicly because of the fear of repercussions.

Tory backbenchers have been more vocal, with Anna Soubry arguing on Monday that new research had underlined the “serious potential perils of pulling out” of either the single market or customs union, inside which EU countries negotiate trade deals collectively.

Soubry, who is supporting the Open Britain campaign for a close relationship with the EU after Brexit, commissioned research from the House of Commons library. It found continued membership of the two groupings would allow the UK to have free trade with countries that buy 90% of its exports.

She said the onus was on Brexit supporters to prove the economic benefits of withdrawal. “The government should bring before parliament serious cost-benefit analysis of the potential impact of leaving both the single market and the customs union. And whether their benefits can really be replicated outside. This must be done before article 50 negotiations start.”

In a sign of continued tension between leave and remain campaigners, the international development secretary, Priti Patel, said that those trying to force a debate and vote on article 50 were trying to “subvert the economic will of the British public”.

Other Brexit supporters, including David Davis and Liam Fox, have hinted at the idea of Britain accepting much looser economic ties with the EU in order to deliver a hard Brexit.

However, the issue of membership of the customs union is also still being considered, the Guardian understands, with a paper on its pros and cons presented at a meeting of May’s Brexit cabinet committee last week.

On migration, Rudd’s suggestion of a visa-entry scheme for skilled workers is not the only option being considered. Under Rudd’s plans, which aim to significantly cut net migration, EU workers would need to have a skilled job before being allowed into Britain.

Although Brexit supporters were reported to have been angered by Hammond’s cautious approach at the meeting, with some accusing him of “arguing like an accountant seeing the risk of everything”, his approach was accepted with ministers leaving all options open.

The Brexit committee includes Hammond, Clark and Green, as well as May, Rudd and the Tory chair – who backed remain – Patrick McLoughlin. But it also has ardent Brexit supporters: David Davis, Boris Johnson, Liam Fox, Priti Patel, Chris Grayling and Andrea Leadsom.

Although May has said that the UK must regain control of its borders and no longer be under the jurisdiction of the European court of justice, she has left a series of other possibilities open, according to sources.

May knows that there are about 20 to 30 Conservative backbenchers who have significant concerns about the direction of the government’s Brexit policy without greater parliamentary scrutiny.

This led Gavin Williamson, the chief whip, to tell the prime minister last week that they could lose the House of Commons vote called by Labour demanding a proper debate on leaving the EU before article 50 is triggered.